Poly(dimethylsiloxane) (PDMS) was investigated as an alternative to Nafion as an air cathode catalyst binder in microbial fuel cells (MFCs). Cathodes were constructed around either stainless steel (SS) mesh or copper mesh using PDMS as both catalyst binder and diffusion layer, and compared to cathodes of the same structure having a Nafion binder. With PDMS binder, copper mesh cathodes produced a maximum power of 1710 ± 1 mW m -2, while SS mesh had a slightly lower power of 1680 ± 12 mW m -2, with both values comparable to those obtained with Nafion binder. Cathodes with PDMS binder had stable power production of 1510 ± 22 mW m -2 (copper) and 1480 ± 56 mW m -2 (SS) over 15 days at cycle 15, compared to a 40% decrease in power with the Nafion binder. Cathodes with the PDMS binder had lower total cathode impedance than those with Nafion. This is due to a large decrease in diffusion resistance, because hydrophobic PDMS effectively prevented catalyst sites from filling up with water, improving oxygen mass transfer. The cost of PDMS is only 0.23% of that of Nafion. These results showed that PDMS is a very effective and low-cost alternative to Nafion binder that will be useful for large scale construction of these cathodes for MFC applications. © 2012 Elsevier B.V.